1. Field of the Invention
The present invention relates to a light scanning apparatus and an image forming apparatus using the same. The present invention is suited to an image forming apparatus using an electrophotographic process, such as a laser beam printer, a digital copying machine, and a multifunction printer.
2. Description of the Related Art
In a known light scanning apparatus, a plurality of light beams emitted from light sources arranged for a plurality of respective colors are deflected by a single rotating polygon mirror, and different photosensitive drums are exposed and scanned using a plurality of imaging optical systems arranged corresponding to the respective light beams.
In such a light scanning apparatus, flare light, which is stray light reflected (scattered) by the surface of an imaging lens and the like included in the imaging optical system during exposure and scanning of the photosensitive drum corresponding to a given color, causes the following problem. Specifically, the flare light may enter the imaging optical system corresponding to a different color, and expose and scan the photosensitive drum corresponding to a color different from the color intended to be exposed and scanned, leading to image defects such as streaks and density unevenness.
The flare light can be suppressed by depositing an antireflection film on the imaging lens. In recent years, however, plastic molded lenses are widely used in order to reduce the weight and the cost of the light scanning apparatus, and hence it is difficult to deposit the antireflection film on a plastic molded lens.
In view of this, in Japanese Patent Application Laid-Open No. 2005-004050, a shielding member configured to shield flare light is arranged in a housing in order to prevent the flare light from reaching a photosensitive drum. However, when the imaging lens or the like is assembled in a position different from a desired position, the optical path of the flare light changes, and hence the flare light may pass by the shielding member. In order to prevent this, the size of the opening portion of the shielding member needs to be reduced as much as possible. However, in this case, the actual light beam that is intended to expose and scan the photosensitive drum may be shielded as well.
Further, in Japanese Patent Application Laid-Open No. 2009-271353, an opening portion of a shielding member is made as narrow as possible by arranging a drive substrate of a motor configured to rotate a rotating polygon mirror in an asymmetric manner in the direction of an optical axis of an imaging lens, and bringing the shielding member as close as possible to the drive substrate. However, the shielding member is close to the drive substrate of the motor, which is a heat source, and hence the shielding member is deformed or displaced in a similar manner to the thermal deformation undergone by the housing, which allows flare light to pass by the shielding member and reach a photosensitive drum. As a result, an image defect is produced. Further, because the shielding member is close to the rotating polygon mirror that is rotating at high speed, unwanted sound, such as wind noise, is a problem.
In this case, when optical components, such as the rotating polygon mirror serving as a deflection element and the imaging lenses, are arranged close together in order to reduce the size of the light scanning apparatus, flare light reflected by the surface of the imaging lenses and the like is again reflected by the top surface (upper surface) of a rotor forming a part of the motor rotatably holding the rotating polygon mirror. The optical path of such flare light (a rotor reflection flare) changes as a result of being reflected by the top surface of the rotor, and moves closer to the actual beam, and thus it is difficult to shield the flare light.
Regarding such a rotor reflection flare, in Japanese Patent Application Laid-Open No. 2009-271384, a gap between the rotor top surface and the rotating polygon mirror lower surface is appropriately set based on the arrangement of the optical components in order to separate the actual light beam and the rotor reflection flare, thereby allowing the rotor reflection flare to be shielded by the shielding member.
In this case, unlike the imaging lenses and the like, the deflection element and the rotor are usually components that can be easily shared by different light scanning apparatus, and hence generally the same deflection element and rotor are used even if the optical specifications are different. However, when those components are shared, optimization of each light scanning apparatus is not always carried out from the perspective of shielding flare light, and hence attempting to optimize each light scanning apparatus can lead to cost increases.